When I beat Sinjid's Shadow, I was a lvl 28 Assassin (apparently the weakest class, but it's nice to be able to keep up with your enemy's speed). For all you people that don't feel like figuring out a decent strategy for yourself, here's how I won (I'll try to be as detailed as possible): Allies: Veradux (lvl 27 in full paladin EXCEPT Judgement weapon) Teco (lvl 25 in full guardian, Judgement and Eternity) And of course myself in full assassin. Setting up my team this way gives me the healing support I need to stay alive, having under 500 health. I also threw all my stat points in Strength. Abilities Used: Max Brutality, Sunder, Master Strike, Coup de Grace, Break 4/5 Blood Focus, 1/3 Block, 1/5 Disruption (used twice) Priorities: 1. If Sinjid's Shadow has 100 Focus, immediately use Disruption. 2. If Sinjid's Shadow uses Shadow Blend, use Break and hope it hits (turns out your high assassin speed helps). One of your teammates might use Electro Bolt. If not, use Block to protect yourself. 3. If the little guys are still alive, might as well take them out. 4. Do damage, using Blood Focus as needed. Make sure you always have enough focus to use Disruption at least once. 5. Repeat step 4 as needed.
Of course, this is just one way to win. Anybody who has improvements feel free to add.
First I tried using Disruption when he recovered his focus. Unfortunately, I missed about 30% of the time.
If you want to beat him without relying on luck, get Block (at least 2/3) and slot it twice. Every time he gets his focus back, use Block. You'll also need Heroic Motivation to heal yourself, Blood Focus and/or Re-Energize to keep your own focus up, and an attack of your choice.
Doing this, you eliminate most of the randomness from the fight, and you basically have a 100% chance of victory. Only heal when 1 more attack would kill you to conserve focus, and use suppression between blocks to lower the need for healing. If your focus does start running low, just stop attacking until it's recovered a bit.
The equipment I used: Full Paladin Set Judgement Power Lantern
This equipment gives a huge amount of total stats. I had over 1000 HP (as a 22 gunslinger), 205 focus, and a total of 281 strength+magic. With that much strength+magic and +100 lightning piercing, Electro Bolt became quite powerful.